If successful, inflatable craft could eventually replace the heavy, inflexible 'metal cans' out of which space stations are currently built.

Nasa said it is possible that the inflatable craft could eventually be used in missions that could take humans back to the Moon - or even to Mars.

When not inflated the capsule is much smaller than space station modules made out of alluminium, meaning it is cheaper to take into space. It carries its own air, but is still much lighter than most craft currently in orbit.

Bigelow Aersospace will built the "space habitat", known as a Bigelow Expandable Activity Module, or Beam.

Above: the Beam module

It will be fitted to the station's Tranquility Node in 2015, brought aboard the eighth SpaceX cargo supply mission, and remain in place for two years.

Astronauts will not regularly live or work in the module, but instead use it as a test to see how it performs in space.

They will gather data on its structural integrity, how much air it leaks into space, and how it deals with radiation, temperature changes and other forms of 'space weather'.

The International Space Station is a uniquely suited test bed to demonstrate innovative exploration technologies like the Beam," said William Gerstenmaier, associate administrator for human exploration and operations at Nasa Headquarters in Washington.

He added:

"As we venture deeper into space on the path to Mars, habitats that allow for long-duration stays in space will be a critical capability. Using the station's resources, we'll learn how humans can work effectively with this technology in space, as we continue to advance our understanding in all aspects for long-duration spaceflight aboard the orbiting laboratory."